Add the polenta to the Instant Pot and pour the chicken stock over. Add the salt and whisk to break up and lumps. Cover and cook on Porridge setting - High Pressure, Normal with a total of 20 minutes.
When done, allow a Natural Release (See Note 3) Release vent value and open lid. Whisk to stir and add the butter and cream. Whisk to incorporate. Add the cheeses and herbs, whisk again until smooth.